Statistical study of seismic and ground pressure oscillations with steady frequencies in the 0.7–5 h period range

Abstract

Abstract. Product spectra of ground pressure variation and seismic oscillations have been calculated in the period subranges of 42-90 min and 2.5-5 h, based on synchronous, colocated microbarograph and seismograph measurements at St. Petersburg (60 • N, 30 • E). The 200 records of 2-3.5 days in length and a combined duration of 525 days have been used. The product spectra have been computed for winter, spring, summer, and autumn, both individually and in combination. The spectra of different seasons are distinct from each other for both microbarograph and seismograph measurements; this can be caused by a seasonal variation in both frequency and amplitude of free oscillations of the atmosphere. There are pressure and seismic oscillations with close frequencies in the spectra for both, for each season and when all seasons are combined. At present, suggestions may only be made regarding the origin of most of these common oscillations. Once again, the penetration of the Earth's free oscillation 0 S 2 with a period of about 54 min into the atmosphere has been confirmed. A common pressure and seismic oscillation with the 206 min period has been detected and has attracted considerable interest. The 159-min periodicity revealed in pressure variations may be associated with the well-known solar oscillation of the 160.01 min period.

Steady-frequency waves at intradiurnal periods from simultaneous co-located microbarometer and seismometer measurements: a case study

“…Analysis of the microbarometer and vertical-pendulum seismometer records shows steady-frequency oscillations at intradiurnal periods up to the ∼0.5 h period, supporting the findings obtained earlier by Karpova et al (2002Karpova et al ( , 2004. There are oscillations lasting for several days that agrees with the observations of waves in the thermosphere by Gerrard et al (2010).…”

“…Besides all the S m subharmonics (m = 4-8), the steadyfrequency oscillations at about 49,54,64,74,77,86, and 91 µHz have simultaneously been detected at two or more sites. The steady-frequency oscillations at 64, 74, and 77 µHz have also been revealed by Karpova et al (2004) through the technique of spectra multiplication. Moreover, the 74 and 77 µHz oscillations have been earlier detected from European superconducting gravimeter measurements (Smylie et al, 1993).…”

“…We adopt the zonal length wave as a measure for the horizontal scale of global waves. If a detected high S m subharmonic is the migrating tide, its zonal wave number s is equal to its number m. The numbers s from 5 to ∼30 are therefore possible for S m at τ ∼ 1-5 h. As for the gravitational normal modes at identical periods, their horizontal configurations are described by the spherical surface functions of degree n from 7 to ∼50 (Karpova et al, 2002). This is also the possible range of s, since s ≤ n. Thus, the horizontal scales of TCs are identical to those of many of the global waves.…”

“…We have analyzed autumn records from 30 August to 3 November 1996 and from 29 August to 4 November 1997. These records also have previously been used by Karpova et al (2002Karpova et al ( , 2004. Because of the technical features of the recorder, each continuous record for both the instruments is limited to week in length.…”

“…However, the meteor radar wind observations near the mesopause (e.g., Forbes et al, 1999b) and satellite measurements of thermospheric density near 200 km (Forbes et al, 1999a) have revealed normal modes up to periods of ∼7 and ∼6 h, respectively. Since both the high S m subharmonics and the normal modes are expected to be transient waves, Karpova et al (2002Karpova et al ( , 2004 have used the technique of multiplication of power spectra for short time series. They have applied this technique to the simultaneous microbarometer and verticalpendulum seismometer measurements at St. Petersburg, simultaneous identical measurements at Schiltach, Germany, and vertical-pendulum seismometer measurements at Collm, Germany.…”